My optimism about Brexit can only have any proof once Brexit has actually happened. I don't need to prove that I am optimistic, I can state it as first hand knowledge.
I'm so sorry that these concepts are so difficult to understand.

My pessimism about Brexit is founded on the plethora of economic and business studies that predict things will be grim. I don't need to prove that I am pessimistic, I can state it as first hand knowledge and have good reason to be so.
I'm so sorry that these concepts are so difficult to understand.

Now stop being so patronising and give us something to offset the pessimism. Other than a blind belief that things will be better.